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Abstract:

The grey-shanked douc monkey (Pygathrix cinerea) is an endemic primate to Vietnam found in 1997. The species is critically endangered with less than 1,000 individuals left in the wild. Research was conducted in Kon Ka Kinh National Park, Gia Lai Province Vietnam for 18 months. The monkeys were found in two forest types: (1) closed evergreen lower montane moist sub-tropical forest; (2) mixed broad-leaf and needle-leaf lower montane moist sub-tropical forest. Group size varied from 2 to 88 individuals; average group size was 14.8 individuals. There were four different social structures found in the encountered groups, including one-male unit (OMU), all-male unit (AMU), multi-male and multi-female group, and solitary group. Annual activity budget involved the monkeys spending the highest proportion of time resting (37.0%) and lowest feeding (11.9%). Seasonality significantly influenced the activity budget result, with increased resting and socialising in the wet season and decreased feeding and travelling. The emergent canopy layer and the main canopy layer in the forest are important for all activities. Trees in the height classes 15-19.9m were very important to the monkeys, since they involved more than 60% of feeding. Branches and boughs were used more often for resting and socialising, while twigs were used more often for feeding and travelling. The monkeys ate 49.5% young leaves, 21.9% ripe fruits, 19.1% unripe fruits and only 9.3% mature leaves. 166 plant species of 40 plant families were identified as foods of the monkeys. The monkeys ate mostly young leaves in the dry season (82%), but switched to fruits (~70%) in the wet season.